All of patents, patent applications, patent publications, scientific articles and the like, which will hereinafter be cited or identified in the present application, will hereby be incorporated by references in their entirety in order to describe more fully the state of the art, to which the present invention pertains.
A dielectric resonator (DR) is used in an oscillator used in a microwave band and in a millimeter wave band for increasing stabilities for a phase noise and the frequency. FIG. 1 is an equivalent circuit showing a configuration of the oscillator using the dielectric resonator (DRO) according to one conventional example. For obtaining a negative resistance, a capacitive micro strip line 28b is connected to a source of transistor FET 14. A micro strip line 28a extending from a gate of transistor FET 14 is inductively coupled with a dielectric resonator 1 having TE01d mode of cylindrical shape. In this configuration, a coupling rate is adjusted by a distance between dielectric resonator 1 and micro strip line 28a. Electromagnetic waves from transistor FET 14 are reflected at a resonant frequency of dielectric resonator 1, and absorbed with termination resistor 15a at a frequency other then the resonant frequency. Therefore, there exists a large negative resistance at the resonant frequency. Matching circuit 16 (which comprises a transmission line and a capacitor) being designed to comply an oscillation condition is connected to a drain of transistor FET 14. Gate bias 17a and drain bias 17b of transistor FET 14 are applied through resistor 15b of several kO and matching circuit 16, respectively. In addition, a resonant frequency is finely tuned by varactor diode 20 connected to one terminal of micro strip line 28c which is inductively coupled with dielectric resonator 1. Capacitor 21a having a low reactance at an operating frequency is connected to one side of varactor diode 20, add resistor 15c having several kO which is DC grounded is connected to the other side. In this configuration, because the resonant frequency of dielectric resonator 1 is determined by an outside dimension of the resonator, a high machining accuracy is required for the resonator. Also, since the coupling rate is tuned by the distance between dielectric resonator 1 and micro strip line 28a, a high positioning accuracy (0.1 mm) of dielectric resonator 1 is required. In addition, as a electromagnetic field is spread out of the resonator, the oscillation frequency is easily changed when the resonator is mounted on a package.
Then, as a bonding structure of a dielectric resonator and a transmission line, a structure shown in FIG. 2 has been proposed in Japanese Laid-open Patent Publication No. 11-145709. FIG. 2 is an exploded perspective view showing a bonding structure of a dielectric resonator and a transmission line according to another conventional example. Dielectric resonator 1 comprises dielectric substrate 30 and conductive plates 29a, 29b. Conductor layers 31a, 31b having circular apertural parts facing to each other are formed on both upper surface and bottom surface of dielectric substrate 30. Dielectric layer 32 is formed on conductive layer 31a using a thin film formation technology. In addition, signal conductive layer 33 is formed on dielectric layer 32. In this configuration, the apertural part of dielectric substrate 30 operates as a resonator. In the Japanese Laid-open Patent Publication No. 11-145709, as with the configuration in FIG. 1, the coupling rate is tuned by a distance between the resonator and signal conductive layer 33. However, because a position of signal conductive layer 33 can be controlled accurately using a thin film formation technology, a variation of the coupling rate is small.
On the other hand, in the example of the Japanese Laid-open Patent Publication No. 11-145709, even though spread of the electromagnetic filed out of the resonator is small compared with a dielectric resonator which has a cylindrical shape, the electromagnetic filed also spreads out upward and bottomward. Therefore, it has been necessary that, for example, lines and a transistor FET other than a resonator, which compose the oscillator, have to be arranged keeping some distance from the resonator. That is, the lines and the transistor FET can not be disposed in upward and bottomward of the resonator, thereby resulting in large size of the circuit. In addition, for the purpose of electrical shielding, conductive plates 29a, 29b covering a resonator portion are separately needed as shown in FIG. 2.